A long range goal of this laboratory is to understand how the enzymic behaviors of vascular endothelial and smooth muscle cells interact to maintain both arterial structural integrity and normal vascular tone. One objective of the work proposed is to determine how the activity of the plasma membrane 5'-nucleotidase (5-ribonucleotide phosphohydrolase, E. C. 3.1.3.5) is regulated in these two cell types. The kinetic properties of the enzyme in cultured arterial smooth muscle cells, in cultured arterial endothelial cells, and in freshly collected endothelial cells will be determined. The rates of synthesis and degradation of enzyme protein will be measured in cultured smooth muscle cells, which maintain in vivo enzyme levels. Endothelial cells in culture lose much of their activity; this loss will be characterized, and a search will be made for factors which promote 5'-nucleotidase activity in cultured endothelial cells. A second objective is to study the synthesis and secretion of angiotensin-converting enzyme by cultured arterial endothelial cells. This protein is found both on the endothelial cell surface in vivo and in vitro, and in soluble form, in plasma and in cell culture medium.